Definition of Buffer Systems
A buffer solution maintains a relatively constant pH upon the addition of small amounts of strong acid or strong base. It contains large, comparable concentrations of a weak conjugate acid-base pair.
Types of Buffer
| Type | Components | pH Range | Example |
|---|---|---|---|
| Acidic buffer | Weak acid + conjugate base (salt) | < 7 | CH₃COOH + CH₃COONa |
| Basic buffer | Weak base + conjugate acid (salt) | > 7 | NH₃ + NH₄Cl |
How an Acidic Buffer Works
Neutralisation of Added Acid
Added \(\text{H}^+\) is consumed by the conjugate base reservoir:
\[\text{CH}_3\text{COO}^-(\text{aq}) + \text{H}^+(\text{aq}) \rightarrow \text{CH}_3\text{COOH}(\text{aq})\]The ratio \([\text{A}^-]/[\text{HA}]\) decreases slightly, producing only a negligible decrease in pH.
Neutralisation of Added Base
Added \(\text{OH}^-\) is neutralised by the weak acid reservoir:
\[\text{CH}_3\text{COOH}(\text{aq}) + \text{OH}^-(\text{aq}) \rightarrow \text{CH}_3\text{COO}^-(\text{aq}) + \text{H}_2\text{O}(\text{l})\]The ratio \([\text{A}^-]/[\text{HA}]\) increases slightly, producing only a negligible increase in pH.
Required Equation Marks in Buffer Explanations
When asked to explain buffer action in an exam, you must state balanced chemical equations for both additions. General descriptive statements without equations will lose marks.
Study this topic on the go
Get active recall flashcards, notes, and topic quizzes in ChemEasy, or build your revision schedule with ChemPlan IB.